Fusion of Active and Passive Waveform Measurements for Mapping the
Hydraulic Fractures
Abstract
Fracture characterization is essential to hydrocarbon and geothermal
exploration and production as well as carbon geo-sequestration. Active
and passive measurements have been extensively applied to map fractures
across various scales. Active and passive measurements have inherent
advantages and limitations that complement each other. In this study, to
improve the mapping of embedded fractures and the surrounding
geomechanically altered regions, we integrate active shear-wave
transmission measurement with passive acoustic-emission measurement
collected during a lab-scale hydraulic-fracturing experiment. The
proposed approach leverages the advantages of the two modalities of
measurements, while minimizing the limitations. Polarized shear-wave
transmission (active) measurement was collected before and after the
hydraulic fracturing, and the acoustic emission (passive) measurement
was collected during hydraulic fracturing. Two sets of two-dimensional
maps of fracture and fracture-induced damage in axial, median and
frontal planes were obtained by separately processing the
physics-informed transformations of active and passive measurements.
These 2D maps are then fed to wavelet-based image-fusion technique to
integrate the two sources of information for the reliable
mapping/imaging of the embedded fractures and the surrounding
geomechanically altered regions. Plain word summary Fractures and
geomechanical alterations embedded in a solid material can be
characterized using active or passive measurements. Signal type, timing,
duration and location of the source is controlled during an active
measurement to allow optimal interactions of the propagating wave and
the fractured material, whereas the signals due to waves generated by
the processes of fracturing and geomechanical alterations are captured
during a passive measurement. Active and passive measurements have
advantages and limitations that complement each other. In this study,
physics-informed transformations and wavelet-based image fusion are used
to integrate the active and passive measurements to get the best of the
two measurement modalities for purposes of reliable imaging of fractures
and the surrounding geomechanically altered regions. Key points
Integration of active and passive measurements will leverage their
strengths and minimize the limitations of individual measurement
techniques. To the best of authors’ knowledge, no reference exists
where the two modalities are combined to characterize the fractures
either in the field or laboratory scale. We integrate active
ultrasonic measurements with passive acoustic-emission measurements
using physics-informed transformations and data fusion techniques. The
proposed method improves the imaging of embedded fractures and the
surrounding geomechanically altered regions. Two-dimensional maps of
fracture and fracturing-induced damage is generated in axial, median and
frontal planes.